Rechargeable battery

ABSTRACT

A rechargeable battery is provided, which includes a protection layer with an inversion plate, thereby improving safety by preventing the inversion plate from malfunctioning. In one example embodiment, the rechargeable battery includes an electrode assembly including a first electrode plate, a second electrode plate, and a separator disposed between the first electrode plate and the second electrode plate, a case accommodating the electrode assembly, and a cap assembly coupled to the case, wherein the cap assembly comprises a cap plate sealing the case and having a short-circuit opening, an inversion plate installed in the short-circuit opening of the cap plate, and a connection plate installed to cover the short-circuit opening of the cap plate, and a protection layer having a higher melting point than the cap plate is formed under the inversion plate.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2014-0043747 filed on Apr. 11, 2014, the content ofwhich is incorporated herein by reference in its entirety.

BACKGROUND

1. Field

Aspects of the present invention relate to a rechargeable battery.

2. Description of the Related Art

A rechargeable battery can be repeatedly charged and discharged, unlikea primary battery that should not be recharged. A low-capacityrechargeable battery packaged in the form of a pack of a battery cell istypically used for a small portable electronic device such as a mobilephone or a camcorder. A large-capacity rechargeable battery havingseveral tens of battery packs connected to each other is widely used asa power supply for driving a motor of a hybrid vehicle and the like.

The rechargeable battery is manufactured in various shapes, andrepresentative shapes thereof may include a cylindrical shape and aprismatic shape. The rechargeable battery is generally configured suchthat an electrode assembly which is formed by interposing a separatorserving as an insulator between positive and negative electrodes, and anelectrolyte solution are housed in a case, and a cap assembly isinstalled in the case.

If excessive heat is generated or an electrolytic solution is decomposedin a rechargeable battery, an internal pressure may be increased, andthere is a risk of ignition or explosion. Accordingly, a rechargeablebattery configured to improve safety is required.

SUMMARY

An aspect of an embodiment of the present invention has been made inview of the above problems, and aspects of embodiments of the presentinvention are directed toward a rechargeable battery that is provided toinclude a protection layer with an inversion plate, thereby improvingsafety by preventing or protecting the inversion plate frommalfunctioning.

According to an embodiment of the present invention, there is provided arechargeable battery including an electrode assembly including a firstelectrode plate, a second electrode plate, and a separator disposedbetween the first electrode plate and the second electrode plate, a caseaccommodating the electrode assembly, and a cap assembly coupled to thecase, wherein the cap assembly includes a cap plate sealing the case andhaving a short-circuit hole, an inversion plate installed in ashort-circuit hole or opening of the cap plate, and a connection plateinstalled to cover the short- circuit hole of the cap plate, and aprotection layer having a higher melting point than the cap plate isformed under the inversion plate.

In the rechargeable battery according to the embodiment of the presentinvention, the protection layer having a relatively high melting pointis formed in the inversion plate, thereby making the inversion platekeep operating even when a short-circuit occurs.

Therefore, the rechargeable battery according to the embodiment of thepresent invention can improve the safety by preventing the inversionplate from malfunctioning by closing a hole generated in the inversionplate due to occurrence of a short-circuit and making the inversionplate continuously operate.

Additional aspects and/or advantages of embodiments of the inventionwill be set forth in part in the description which follows and in partwill be obvious from the description or may be learned by practice ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The aspects, features and advantages of the present invention will bemore apparent from the following detailed description in conjunctionwith the accompanying drawings, in which:

FIG. 1 is a perspective view of a rechargeable battery according to anembodiment of the present invention;

FIG. 2 is a cross-sectional view of the rechargeable battery taken alongthe line I-I′ of FIG. 1;

FIG. 3A is an enlarged cross-sectional view illustrating a portion ‘A’of FIG. 2 and FIG. 3B is a cross-sectional view illustrating a casewhere an inversion plate shown in FIG. 3A makes contact with a terminalplate;

FIG. 4A is a perspective view illustrating an inversion plate and aprotection layer shown in FIG. 2 and FIG. 4B is a rear view illustratinga bottom portion of the inversion plate having a protection layer ofFIG. 4A;

FIG. 5 is a cross-sectional view illustrating a state in which theinversion plate shown in FIG. 4B is stacked;

FIG. 6 is an enlarged cross-sectional view illustrating a portion of arechargeable battery according to another embodiment of the presentinvention, corresponding to the portion ‘A’ of FIG. 2;

FIG. 7 is an enlarged cross-sectional view illustrating a portion of arechargeable battery according to still another embodiment of thepresent invention, corresponding to the portion ‘A’ of FIG. 2; and

FIG. 8 is an enlarged cross-sectional view illustrating a portion of arechargeable battery according to still another embodiment of thepresent invention, corresponding to the portion ‘A’ of FIG. 2.

DETAILED DESCRIPTION

Hereinafter, examples of embodiments of the invention will be describedin detail with reference to the accompanying drawings such that they caneasily be made and used by those skilled in the art.

FIG. 1 is a perspective view of a rechargeable battery according to anembodiment of the present invention, FIG. 2 is a cross-sectional view ofthe rechargeable battery taken along the line I-I′ of FIG. 1, FIG. 3A isan enlarged cross-sectional view illustrating a portion ‘A’ of FIG. 2,FIG. 3B is a cross-sectional view illustrating a case where an inversionplate shown in FIG. 3A makes contact with a terminal plate, FIG. 4A is aperspective view illustrating an inversion plate and a protection layershown in FIG. 2, FIG. 4B is a rear view illustrating a bottom portion ofthe inversion plate having a protection layer of FIG. 4A, and FIG. 5 isa cross-sectional view illustrating a state in which the inversion plateshown in FIG. 4B is stacked.

Referring to FIGS. 1 and 2, the rechargeable battery 100 according to anembodiment of the present invention includes an electrode assembly 10, afirst collector plate 20, a second collector plate 30, a case 40, and acap assembly 50.

The electrode assembly 10 may be formed by winding or laminating astacked structure including a first electrode plate 11, a separator 13,and a second electrode plate 12. In an implementation, the firstelectrode plate 11 may serve as a positive electrode and the secondelectrode plate 12 may serve as a negative electrode.

The first electrode plate 11 may be formed by coating a first electrodeactive material (made of, e.g., a transition metal oxide) on a firstelectrode collector (made of a metallic foil, e.g. aluminum foil) andmay include a first electrode uncoated portion 11 a that is not coatedwith the first electrode active material. The first electrode uncoatedportion 11 a may become a path of current flow between the firstelectrode plate 11 and an outside of the first electrode plate 11. Incertain embodiments of the present invention, the material of the firstelectrode plate 11 is not limited to those listed herein.

The second electrode plate 12 may be formed by coating a secondelectrode active material (made of, e.g., graphite or a carbon material)on a second electrode collector (made of a metallic foil, e.g., copperor nickel) and may include a second electrode uncoated region or portion12 a that is not coated with the second electrode active material. Thesecond electrode uncoated portion 12 a may become a path of current flowbetween the second electrode plate 12 and an outside of the secondelectrode plate 12. In certain embodiments of the present invention, thematerial of the second electrode plate 12 is not limited to those listedherein.

The first electrode plate 11 and the second electrode plate 12 may havedifferent polarities. That is to say, the first electrode plate 11 mayserve as a negative electrode and the second electrode plate 12 mayserve as a positive electrode.

The separator 13 may prevent an electric short between the firstelectrode plate 11 and the second electrode plate 12 and may allow onlylithium ions to pass. The separator 13 may be formed from, e.g.,polyethylene (PE), polypropylene (PP) or a composite film ofpolyethylene (PE) and polypropylene (PP). The material of the separator13 is not limited to those listed herein.

A first collector plate 20 and a second collector plate 30, which areelectrically connected to the first electrode plate 11 and the secondelectrode plate 12, respectively, may be coupled to (e.g., connectedwith or to) opposite ends of the electrode assembly 10.

The first collector plate 20 may be made of a conductive material, suchas aluminum, and may make contact with the first electrode uncoatedportion 11 a protruding to one end of the electrode assembly 10 to beelectrically coupled to or electrically connected with (e.g., connectedto) the first electrode plate 11. The first collector plate 20 mayinclude a first connection part 21, a first extension part 23, a firstterminal hole or opening 24 and a fuse part 25.

The first connection part 21 is installed between a top portion of theelectrode assembly 10 and a bottom portion of the cap assembly 50 and isshaped as a plate. Here, the first terminal hole 24 and the fuse part 25are formed in the first connection part 21.

The first extension part 23 is bent with respect to the first connectionpart 21, extends from an end of the first connection part 21 and isshaped as a plate substantially contacting the first electrode uncoatedportion 11 a. Here, assuming that a corner at which the first connectionpart 21 and the first extension part 23 meet is denoted by referencecharacter ‘C’, the first connection part 21 and the first extension part23 may be perpendicular to each other about the corner C.

The first terminal hole 24 is formed at one side of the first connectionpart 21 and provides for a space in the first connection part 21, intowhich a first electrode terminal 52 of the cap assembly 50 is fitted andcoupled.

The fuse part 25 is formed on the top portion of the electrode assembly10 so as not to make contact with an electrolytic solution, which is forthe purpose of preventing the electrolytic solution from igniting due toheat generated from the fuse part 25. Here, the fuse part 25 (and/or anopening for housing the fuse part 25) is formed at a region of the firstconnection part 21 adjacent to the corner C so as not to overlap withthe first electrode terminal 52 coupled to the first terminal hole 24.The fuse part 25 may be melted or softened due to heat generated by alarge amount of current flowing due to a short circuit occurring to therechargeable battery 100, thereby functioning as a fuse that blocks theflow of current. Here, the short circuit may be caused due to a contactbetween the inversion plate 60 and the second terminal plate 56 whenheat is generated due to over-charge of the rechargeable battery 100 andan electrolytic solution is decomposed to make the internal pressure ofthe rechargeable battery 100 exceed a preset pressure. Accordingly, thefuse part 25 is melted due to a short circuit during over-charge, andblocks the flow of current, thereby interrupting charging or dischargingof the rechargeable battery 100 before the rechargeable battery 100comes to a dangerous situation, such as ignition or explosion.

The second collector plate 30 may be made of a conductive material, suchas nickel or copper and may make contact with the second electrodeuncoated portion 12 a protruding to the other end of the electrodeassembly 10 to then be electrically connected to the second electrodeplate 12. The second collector plate 30 may include a second connectionpart 31, a second extension part 33 and a second terminal hole 34.

The second collector plate 30 may not include a fuse part correspondingto the fuse part 25 of the first collector plate 20 shown in FIG. 2because the first collector plate 20 of the embodiment of the presentinvention includes the fuse part 25 functioning as a fuse. In addition,the first collector plate 20 made of, for example, aluminum, has a lowermelting point than the second collector plate 30 made of, for example,nickel or copper, thereby more easily implementing the fuse function.

The case 40 may be made of a conductive metal, such as aluminum, analuminum alloy, or nickel plated steel, and may have a substantiallyhexahedral shape having an opening through which the electrode assembly10, the first collector plate 20, and the second collector plate 30 areinserted and arranged. Although the opening is not illustrated in FIG.2, the case 40 and the cap assembly 50 of the present embodiment areshown in an assembled state. Thus, the peripheral portion of the capassembly 50 substantially corresponds to the opening in the case 40.Meanwhile, the interior surface of the case 40 is insulated, so that thecase 40 is electrically insulated from the electrode assembly 10, thefirst collector plate 20, the second collector plate 30 and the capassembly 50. Here, the case 40 may have a polarity, so that it functionsas a positive electrode, for example. In addition, the case 40 mayinclude an electrolytic solution containing a carbonate-based solventexemplified by dimethyl carbonate (DMC), diethyl carbonate (DEC),dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropylcarbonate (EPC), methylethyl carbonate (MEC) ethylene carbonate (EC),propylene carbonate (PC), butylene carbonate (BC), and so on, but notlimited thereto.

The cap assembly 50 is coupled to the case 40. In more detail, the capassembly 50 includes a cap plate 51, a first electrode terminal 52, asecond electrode terminal 53, a gasket 54, a first terminal plate 55,and a second terminal plate 56. In addition, the cap assembly 50 mayfurther include a plug 57, a vent plate 58, an upper insulating member59 a, a connecting plate 59 b, an inversion plate 60, a lower insulatingmember 63, and a protection layer 70.

The cap plate 51 seals the opening of the case 40 and may be made of thesame material as the case 40. In the present embodiment, the cap plate51 may have the same polarity as the case 40.

The first electrode terminal 52 penetrates through the cap plate 51 atone side of the cap plate 51 and is electrically coupled to the firstcollector plate 20. The first electrode terminal 52 may have a pillarshape. An upper pillar exposed to an upper portion of the cap plate 51is coupled to the first terminal plate 55 by riveting and has aprotrusion part 52 b formed thereat to prevent the first electrodeterminal 52 from being dislodged from the cap plate 51.'A lower pillarpositioned below the cap plate 51 has a flange 52 a formed thereat toprevent the first electrode terminal 52 from being dislodged from thecap plate 51. A portion of the first electrode terminal 52 positioned ata lower portion of the flange 52 a is fitted into the first terminalhole 24 of the first collector plate 20. Here, the first electrodeterminal 52 may be electrically coupled to the cap plate 51.

The second electrode terminal 53 penetrates through the cap plate 51 atthe other side of the cap plate 51, and is electrically coupled to thesecond collector plate 30. Since the second electrode terminal 53 hassubstantially the same shape as the first electrode terminal 52, adescription thereof will not be repeated. However, the second electrodeterminal 53 may be electrically insulated from the cap plate 51.

The gasket 54 is formed of an insulating material and is located betweenthe first electrode terminal 52 and the cap plate 51 and between thesecond electrode terminal 53 and the cap plate 51 to seal respectivegaps between the cap plate 51 and each of the first and second electrodeterminals 52 and 53. The gasket 54 prevents permeation of externalmoisture into the rechargeable battery 100 or leakage of electrolytefrom the inside of the rechargeable battery 100.

The first terminal plate 55 is coupled to the upper pillar of the firstelectrode terminal 52 by riveting to fix the first electrode terminal 52with the cap plate 51.

The second terminal plate 56 is coupled to the upper pillar of thesecond electrode terminal 53 by riveting to fix the second electrodeterminal 53 with the cap plate 51. The second terminal plate 56 isformed to allow the second electrode terminal 53 to be fitted thereintofrom an exterior side spaced apart from the cap plate 51, that is, abovethe upper insulating member 59 a and extends to cover a short-circuithole or opening 51 c. The second terminal plate 56 is electricallyconnected to the second electrode terminal 53. In addition, the secondterminal plate 56 has a protrusion part 56 a located to correspond to around part 61 of the inversion plate 60. The protrusion part 56 a isformed to protrude toward the inversion plate 60. In addition, theprotrusion part 56 a has a smaller diameter than the round part 61 ofthe inversion plate 60. The protrusion part 56 a may be shaped as ahollow cylinder, but the shape of the protrusion part 56 a is notlimited thereto. The second terminal plate 56 causes a short circuit dueto a contact with the inversion plate 60 that upwardly convexlyprotrudes when the internal pressure of the rechargeable battery 100exceeds a preset pressure due to a high-voltage disconnection occurringin a state in which it is connected to an external battery or heatgenerated by over-charge conditions or electrolyte decomposition. If theshort circuit is caused to the rechargeable battery 100 by the secondterminal plate 56, a large amount of current flows in the rechargeablebattery 100 and heat is generated. In this case, the fuse part 25functions as a fuse, thereby improving the safety of the rechargeablebattery 100.

The plug 57 seals an electrolyte injection hole 51 a of the cap plate51. The vent plate 58 is installed in a vent hole 51 b of the cap plate51 and has a notch 58 a formed to be opened at a set or predeterminedpressure.

The upper insulating member 59 a is formed to be fitted between thesecond electrode terminal 53 and the cap plate 51 and makes tightcontact with the cap plate 51 and the gasket 54. The upper insulatingmember 59 a insulates the second electrode terminal 53 and the cap plate51 from each other.

The connecting plate 59 b is formed to be fitted between the firstelectrode terminal 52 and the cap plate 51 and makes tight contact withthe cap plate 51 and the gasket 54 through a nut. The connecting plate59 b electrically connects the first electrode terminal 52 and the capplate 51 to each other.

The lower insulating member 59 c is formed between the cap plate 51 andeach of the first collector plate 20 and the second collector plate 30and prevents an unnecessary short circuit from occurring therebetween.

The inversion plate 60 is installed in the short-circuit hole or opening51 c of the cap plate 51 between the upper insulating member 59 a andthe cap plate 51 by welding. The inversion plate 60 includes adownwardly convex round part 61 (facing the inside of the case, that is,in a direction toward the electrode assembly) and a flange part 62 fixedto the cap plate 51.

The inversion plate 60 may be inverted to then upwardly convexlyprotrude when the internal pressure of the rechargeable battery 100exceeds a preset pressure due to a high-voltage disconnection occurringin a state in which it is connected to an external battery or heatgenerated by over-charge conditions or electrolyte decomposition. Theinversion plate 60 is inverted to be brought into contact with theprotrusion part 56 a of the second terminal plate 56, thereby causing ashort circuit. The fuse part 25 is broken by the short circuit, therebyinterrupting charging or discharging of the rechargeable battery 100before the rechargeable battery 100 comes to a dangerous situation, suchas ignition or explosion. That is, the inversion plate 60 causes aninternal short circuit to the rechargeable battery 100 to melt the fusepart 25 in order to block the flow of current, thereby increasing thesafety of the rechargeable battery 100. Therefore, in order to preventthe rechargeable battery 100 from being stably charged or dischargedwhen a short circuit is generated in the rechargeable battery 100, acontact between the inversion plate 60 and the second terminal plate 56should be maintained before the fuse part 25 is melted. Here, theinversion plate 60 and the second terminal plate 56 are maintained at aline contacting state or a point contacting state.

Meanwhile, the inversion plate 60 and the cap plate 51 have the samepolarity. The inversion plate 60 may be made of aluminum, but notlimited thereto.

As shown in FIG. 5, multiple inversion plates 60 are stacked for storagebefore they are applied to an automated process for assembling therechargeable battery 100. However, friction between the stackedinversion plates 60 may occur, resulting in scratches on surfaces of thestacked inversion plates 60. Accordingly, when heat is generated due toover-charge of the rechargeable battery 100 and an electrolytic solutionis decomposed to make the internal pressure of the rechargeable battery100 exceed a preset pressure, each of the inversion plates 60 and thesecond terminal plate 56 are brought into contact with each other. Inthis case, the inversion plates 60 may not be properly inverted due tothe scratches. Alternatively, gases generated in the rechargeablebattery 100 may be exhausted through crevices of the scratches, therebyreducing or preventing the inversion plates 60 from being furtherinverted. Therefore, the contact between the inversion plate 60 and thesecond terminal plate 56 may not be maintained. In the presentinvention, a protection layer 70 is formed under each of the inversionplates 60, thereby minimizing friction between the stacked inversionplates 60 and ultimately preventing scratches from being generated onthe inversion plates 60.

In addition, when contact resistance between the inversion plate 60 andthe protrusion part 56 a of the second terminal plate 56 is higher thanthe resistance of the fuse part 25, the inversion plate 60 maymalfunction, so that it cannot completely break the fuse part 25,thereby causing damages to the inversion plate 60 and the secondterminal plate 56. Here, even when the inversion plate 60 is damaged,the fuse part 25 can be broken just by maintaining the contact betweenthe inversion plate 60 and the protrusion part 56 a of the secondterminal plate 56. However, since the gases generated in therechargeable battery 100 are exhausted to the outside of the case 40through damages to parts of the inversion plate 60, the inversion plate60 may not be further inverted. Consequently, when malfunctioning occursto the inversion plate 60, the safety of the rechargeable battery 100may be impaired. In the present invention, the inverting operation ofthe inversion plate 60 can be maintained by covering the damaged partsof the inversion plate 60 by forming the protection layer 70 under theinversion plate 60 even when the inversion plate 60 is partiallydamaged.

The protection layer 70 is formed on one surface of the inversion plate60. That is, the protection layer 70 is formed to entirely surroundand/or cover a bottom surface of the round part 61 of the inversionplate 60. The protection layer 70 is formed by adhering or coating anappropriate material to the bottom surface of the round part 61. Theprotection layer 70 is made of a material having a higher melting pointthan the inversion plate 60. In the present invention, since theprotection layer 70 is formed of a material having a higher meltingpoint than the inversion plate 60, the damaged parts of the inversionplate 60 are covered until the fuse part 25 is broken. In addition, theprotection layer 70 is made of a material not causing a chemicalreaction when it is brought into contact with an electrolytic solutioncontained in the case 40.That is, when the inversion plate 60 is made ofaluminum having a melting point of approximately or about 600° C., theprotection layer 70 may have a melting point of approximately or about600° C. or higher and may be made of a material not reacting with theelectrolytic solution. In one embodiment, the protection layer 70 may bemade of polyimide (PI). The PI is a resin having high heat resistanceand a good electric insulating property and has a melting point ofapproximately 700° C. In addition, the PI is a material that does notreact with the electrolytic solution contained in the case 40.Therefore, the protection layer 70 having a higher melting point thanthe inversion plate 60 is formed in the inversion plate 60, therebyallowing the inversion plate 60 to be continuously inverted when a shortcircuit occurs to the rechargeable battery 100 of the present invention.

Meanwhile, in the present invention, the protection layer 70 made of PIis exemplified, but aspects of the present invention are not limitedthereto. Any material can be used for forming the protection layer 70 aslong as it has a higher melting point than the inversion plate 60 anddoes not react with the electrolytic solution contained in the case 40.

Next, a rechargeable battery according to another embodiment of thepresent invention will now be described with reference to FIGS. 6 to 8.

FIG. 6 is an enlarged cross-sectional view illustrating a portion of arechargeable battery according to another embodiment of the presentinvention, corresponding to the portion ‘A’ of FIG. 2. FIG. 7 is anenlarged cross-sectional view illustrating a portion of a rechargeablebattery according to still another embodiment of the present invention,corresponding to the portion ‘A’ of FIG. 2, and FIG. 8 is an enlargedcross-sectional view illustrating a portion of a rechargeable batteryaccording to still another embodiment of the present invention,corresponding to the portion ‘A’ of FIG. 2.

The rechargeable battery 100 according to another embodiment of thepresent invention is substantially the same with the rechargeablebattery 100 shown in FIG. 2 in view of configuration and functions,except for a shape of a protection layer 70 formed on a bottom surfaceof an inversion plate 60. Accordingly, in the rechargeable battery 100according to another embodiment of the present invention, descriptionsof the same components as those of the rechargeable battery 100 shown inFIG. 2 will not be repeated, and the following description will focus onthe protection layer 70 formed on the bottom surface of the inversionplate 60.

Referring to FIG. 6, the protection layer 170 is shaped to correspond toa protrusion part 156 a of a second terminal plate 156. In more detail,the protection layer 170 is formed on the bottom surface of theinversion plate 160 to have a shape corresponding to a shape of theprotrusion part 156 a of the second terminal plate 156, that is, acircular ring shape. The protection layer 170 covers the inversion plate160 substantially contacting the protrusion part 156 a of the secondterminal plate 156. Here, an outer diameter D2 of the protrusion part156 a of the second terminal plate 156 is in one embodiment smaller thanan outer diameter D1 of the circular ring-shaped protection layer 170(that is, an outer side distance between a left-side protection layer171 and a right-side protection layer 172 on a cross section of theprotection layer 170). In addition, in order to cover a region of theinversion plate 160 contacting the protrusion part 156 a of the secondterminal plate 156, an inner diameter of the protrusion part 156 a ofthe second terminal plate 156 is in one embodiment larger than that ofthe protection layer 170. In the present embodiment, the protectionlayer 170 shaped to correspond to the protrusion part 156 a of thesecond terminal plate 156 making contact with the inversion plate 160 isformed on the bottom surface of the inversion plate 160 to cover theregion of the inversion plate 160 contacting the protrusion part 156 aof the second terminal plate 156, thereby maintaining the invertingoperation of the inversion plate 160.

Referring to FIG. 7, a protection layer 270 is formed only on a regionexcept for a central region of a bottom surface of an inversion plate260. In more detail, the protection layer 270 is formed only on aregion, except for a region of the bottom surface of the inversion plate260 having a smaller inner diameter D3 than an inner diameter D4 of theprotrusion part 256 a of the second terminal plate 256. That is, theprotection layer 270 is shaped as a circular ring having a relativelylarge width to be formed only on a region of the bottom surface of theinversion plate 260, where an inner diameter of the region is greaterthan or equal to that of the protrusion part 256 a of the secondterminal plate 256. In the protection layer 270 according to the presentembodiment, the inversion plate 260 may be formed to have a circularring shape. The protection layer 270 covers the region except for thecentral region of the bottom surface of the inversion plate 260, thecentral region not making contact or overlap with the protrusion part256 a of the second terminal plate 256. When the internal pressure ofthe rechargeable battery 100 exceeds a preset pressure due to ahigh-voltage disconnection occurring in a state in which it is connectedto an external battery or heat generated by over-charge conditions orelectrolyte decomposition, the central region of the inversion plate 260is pushed by the internal gases, thereby easily performing the invertingoperation of the inversion plate 260. In addition, the protection layer270 covers the region of the inversion plate 260 making contact with theprotrusion part 256 a of the second terminal plate 256 (that is, theregion except for the central region by forming the protection layer 270on the region except for the central region), thereby maintaining theinverting operation of the inversion plate 260.

Referring to FIG. 8, a protection layer 370 is formed on a region of abottom surface of an inversion plate 360 shaped to correspond to aprotrusion part 356 a of the second terminal plate 356 more thickly thanin a peripheral region of the region of the bottom surface of theinversion plate 360. In more detail, the protection layer 370 is formedon the region of the bottom surface of the inversion plate 360 shaped tocorrespond to the protrusion part 356 a of the second terminal plate 356more thickly than in other peripheral regions. The protection layer 370covers the inversion plate 360 substantially contacting the protrusionpart 356 a of the second terminal plate 356. In the present embodiment,the protection layer 370 that is thicker than its peripheral region isformed on the region of the bottom surface of the inversion plate 360shaped to correspond to the protrusion part 356 a of the second terminalplate 356 to cover the region of the inversion plate 360 making contactwith the protrusion part 356 a of the second terminal plate 356, therebymaintaining the inverting operation of the inversion plate 360.

Although the present invention has been described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that a variety of modifications and variations may bemade to the present invention without departing from the spirit or scopeof the present invention defined in the appended claims, and theirequivalents.

What is claimed is:
 1. A rechargeable battery comprising: an electrode assembly comprising a first electrode plate, a second electrode plate, and a separator disposed between the first electrode plate and the second electrode plate; a case accommodating the electrode assembly; and a cap assembly coupled to the case, wherein: the cap assembly comprises a cap plate sealing the case and having a short- circuit opening, an inversion plate installed in the short-circuit opening of the cap plate, and a connection plate installed to cover the short-circuit opening of the cap plate, and a protection layer having a higher melting point than the cap plate is formed under the inversion plate.
 2. The rechargeable battery of claim 1, wherein the protection layer is made of a material configured to not cause a chemical reaction when it is brought into contact with an electrolytic solution contained in the case.
 3. The rechargeable battery of claim 1, wherein the protection layer is made of polyimide (PI).
 4. The rechargeable battery of claim 1, wherein the inversion plate comprises a downwardly convex round part and a flange part fixed to the cap plate.
 5. The rechargeable battery of claim 1, wherein the connection plate has a protrusion part located to correspond to the inversion plate.
 6. The rechargeable battery of claim 5, wherein the protrusion part is formed to face the inversion plate.
 7. The rechargeable battery of claim 5, wherein the protection layer is shaped to correspond to the protrusion part.
 8. The rechargeable battery of claim 5, wherein the protrusion part has a smaller outer diameter than that of the protection layer.
 9. The rechargeable battery of claim 5, wherein the protection layer is formed only on a region except for a region of a bottom surface of the inversion plate having a smaller inner diameter than that of the protrusion part.
 10. The rechargeable battery of claim 5, wherein the protection layer is formed on a region of a bottom surface of the inversion plate shaped to correspond to the protrusion part more thickly than in a peripheral region of the region of the bottom surface of the inversion plate.
 11. The rechargeable battery of claim 1, wherein the protection layer is formed only on a region except for a central region of a bottom surface of the inversion plate.
 12. A method of forming a rechargeable battery, the method comprising: providing an electrode assembly by disposing a separator between a first electrode plate and a second electrode plate; accommodating the electrode assembly in a case; and coupling a cap assembly to the case, wherein the cap assembly comprises a cap plate sealing the case and having a short-circuit opening, an inversion plate installed in the short-circuit opening of the cap plate, and a connection plate installed to cover the short-circuit opening of the cap plate, and a protection layer having a higher melting point than the cap plate is formed under the inversion plate.
 13. The method of claim 12, wherein the protection layer is made of a material not causing a chemical reaction when it is brought into contact with an electrolytic solution contained in the case.
 14. The method of claim 12, wherein the protection layer is made of polyimide (PI).
 15. The method of claim 12, wherein the connection plate has a protrusion part located to correspond to the inversion plate.
 16. The method of claim 15, wherein the protrusion part is formed to face the inversion plate.
 17. The method of claim 15, wherein the protection layer is shaped to correspond to the protrusion part.
 18. The method of claim 15, wherein the protrusion part has a smaller outer diameter than that of the protection layer.
 19. The method of claim 15, wherein the protection layer is formed only on a region except for a region of a bottom surface of the inversion plate having a smaller inner diameter than that of the protrusion part.
 20. The method of claim 15, wherein the protection layer is formed on a region of a bottom surface of the inversion plate shaped to correspond to the protrusion part more thickly than in a peripheral region of the region of the bottom surface of the inversion plate. 